Abstract:

Northeast Pacific Ocean sediments were analyzed to determine the past
relationship between northeast Pacific sea surface conditions and the climate on the
adjacent continent, the Pacific Northwest of North America. Studies of modern
ocean-atmosphere interactions demonstrate the significant effect sea surface conditions
and atmospheric circulation in the Northeast Pacific Ocean has on the climate of the
west coast of North America. Thus, it is likely that past continental climate change
can be correlated to changes in sea surface temperature in the northeast Pacific Ocean.
We analyzed radiolaria from twelve sediment cores, ranging from 33.62°N to
54.42°N latitude along the west coast of North America to reconstruct past sea surface
conditions. Relationships between modern radiolaria and mean annual sea surface
temperature calibrate equations used to estimate sea surface conditions for the past
20,000 years. Chronology is controlled by radiocarbon ages from planktonic
foraminifera and bulk organic carbon.
The reconstructions of sea surface conditions from changes in radiolaria
assemblages indicate that the upwelling center off the west coast of North America
was further south 15,000 years ago than it is today, and reached its present location
13,000 years ago. We infer that the West Wind Drift and Transition Zone were
further south in the latest Pleistocene as a result of a more southerly North Pacific
High pressure cell prior to 13,000 years ago.
Two Pacific Northwest continental records of paleotemperature are well
correlated to the sea surface temperature record the northeast Pacific around 48N
latitude, with temperatures increasing over the past 20,000 years. Significant
temperature minima and glacial expansions occurred at 13,000 and 4,000 years ago in
the records examined, as did a minor minimum at 16,000 years ago. We conclude
that changes in the past latitudinal position of the West Wind Drift played a significant
role in controlling continental climate immediately to its east, as it does in the present
day environment.